Vacuum pumping system



Jan. 5, 1965 J. T- WELBOURN VACUUM PUMPING SYSTEM Filed July 10, 1962 2 Sheets-Sheet 1 fmik ' INVENTOR. Jbl-IN 7. WELO RN Jan. 5, 1965 J. T. WELBOURN VACUUM PUMPING SYSTEM Filed July 10, 1962 2 Sheets-Sheet 2 INVENTOR. JoH/v 7. Wm u/w United States Patent ()fiice ilfi ifiz i atented Jan. 5, 1965 3,164,320 VACUUM PUMPING SYSTEM John T. Welbourn, Xenia, Ohio, assignor to the United States of America as represented by the Secretary of the Air Force Filed July 10, 1962, Ser. No. 208,973 2 Claims. (Cl. 23069) (Granted under Title 35, US. Code (E52), sec. 266) The invention described herein may be manufactured and used by or for the United States Government for governmental purposes Without payment to me of any royalty thereon.

This invention relates to a method and apparatus for pumping large volumes of gaseous material. In a more particular aspect, this invention concerns itself with a system for converting a gaseous material into a solid through the medium of a chemical reaction whereby large volumes of the gaseous material can be pumped or removed at high speeds from a closed system with the concurrent production of very low pressures within the system.

The testing and analysis of satellite and space vehicle propulsion systems often requires the utilization of very low vacuums and low temperatures of about 20 K. Heretofore, it was necessary to employ a number of large, mechanical and diffusion pumps in series in order to produce the desired vacuums. In addition to the problem of producing low vacuums and temperatures for test purposes the propulsion systems evolve large volumes of hydrogen gas which must be removed from the test facilities. High vacuum mechanical pumps, unless used in series, do not have the appreciable capacity necessary to remove the large volumes of hydrogen that are evolved during testing. Cryogenic pumps, ion pumps and gettering type pumps, all of which are primarily mechanical in nature, also are lacking in the necessary capacity.

For example, in the testing of arc-jet engines, which are suitable for space travel, vacuums in the range of 1 mm. of mercury are required. In order to evacuate the large volumes of hydrogen ejected from the arc-jet, very large positive displacement booster pumps and mechanical high vacuum pumps (above 20,000 c.f.m.) have to be used in series and parallel. In accordance with the teachings of this invention, however, the need for booster pumps to remove the large volumes of hydrogen is eliminated. This permits the use of quite small vacuum pumps, which are required only for the initial pump down. Accordingly, conventional, low cost, readily available equipment can be used for obtaining and maintaining vacuums in the range of pressures from 0.1 mm. to mm. of mercury without the use of expensive booster pumps in series with high vacuum mechanical pumps. This becomes especially significant, where large volumes of hydrogen must be removed from an evacuated vessel or system within a short period of time.

In general, this invention involves a system for vacuum pumping large volumes of gaseous material by means of the chemical reaction of a gaseous element, which is to be pumped, with one or more elements of a gaseous, liquid or solid chemical compound in order to'produce a third vaporous chemical compound, the vapors of which can be frozen into a solid at a much higher temperature than the original gas and at a vapor pressure low enough to satisfy the requirements of the system application.

Accordingly, it is the primray object of this invention to provide a novel system for producing a high vacuum.

Another object of this invention is to provide a novel system for pumping large volumes of gaseous material at high pumping speeds.

Still another object of this invention is to provide a novel system especially suitable for removing extremely hot gases.

A further object of this invention is to provide a novel system for pumping large volumes of gaseous material at the low pressures usually considered to be in the medium or high vacuum ranges without the use of large and expensive booster pump units in series with high vacuum mechanical pumps.

Still a further object of this invention is to provide a novel system for vacuum pumping large volumes of gaseous materials by means of a chemical reaction rather than through the use of mechanical means whereby the pumping action is accomplished as a result of the chemical reaction.

The novel features which are believed to be characteristic of the invention are set forth in the appended claims. However, specific embodiments of the invention, both as to their organization and method of operation, together with further objects, advantages and features thereof, may best be understood by reference to the following detailed description taken in conjunction with the accompanying drawings in which:

FIGURE 1 is a schematic view partly in section which illustrates one specific embodiment of this invention; and

FIGURE 2 is a schematic view partly in section which illustrates a further specific embodiment of the invention.

Referring to FIGURE 1, there is depicted a propulsion device under test operating conditions such as an arcjet 19 from which large volumes of hydrogen gas 12 are evolved. In order to effect removal of the hydrogen gas 12, the chamber 14 is initially evacuated by means of a relatively small mechanical pump 16 While the shut-off valve 18 remains open. The valve 18 is then closed and a stream of oxygen 20 from a suitable supply source 22 is admitted through valve 24, oxygen pressure regulator 26, and calibrated fiowmeter 28 until the desired operating pressure is reached, as shown by a vacuum gauge, not illustrated, which is connected to the chamber 14. A small flow of hydrogen gas 12 from a suitable source of supply 30 passes through valve 32, hydrogen pressure regulator 34 and a calibrated flow meter 36. Electrical power, from a suitable source not shown, is turned on and flows through the arc-jet device 10. This produces a hot jet of hydrogen gas 12 which is discharged into evacuated chamber 14. The hot hydrogen gas 12 immediately combines with the oxygen 20 and produces water vapor.

A pressure recovery section 38 permits the testing of arc-jets with higher flow rates and at lower pressures than otherwise possible. However, it is not essential to the operation or functioning of the pumping system of this invention. It the pressure recovery system is used, however, it may be water-cooled and partially or completely eliminate the need for a high temperature heat exchanger as shown at 40. The design features of the heat exchanger 40 are not critical and any suitable device may be employed. For example, a water-cooled flat plate, a series of coils or a number of tubes have been found to be suitable. The only requirement is that the hot gases come in contact with a surface from which heat is being removed continually by means of a fluid which circulates through the heat exchanger 40. The heat transfer fluid flows from :a suitable source not shown through the heat exchange 40 by means of inlet and outlet tubes 42 and 414 respectively. Although the high temperature heat exchanger 40 is not essential to the invention, its use is desirable since it aids in reducing the load on the low temperature heat exchanger 46.

The heat exchanger 46 may also be of conventional construction provided it has a comparatively large surface area which can be kept at a sufiiciently low temperature to freeze the water vapor into ice and maintain the ice at a temperature such that its vapor pressure is reasonably below the pressure desired in the chamber 14.

A refrigerant for lowering the temperature of the surfaces of the heat exchanger 46 flows from a suitable source not shown through inlet tube 48 and outlet tube 50. An extremely desirable refrigerant, and one which has been found to be especially suitable for the operation ofinvention, is, a, cryogenic fluid such as nitrogen'which has a boiling point of 77 K.

During operation of the above-described embodimerit of this'invention, the oxygen and hydrogen gases are allowed to flow into the chamber 14. in stoichiometric proportions in order to produce the desired water vapor, which in turn is, frozen into a solid by freezing the water vapor. The effect produced by the process of this invention is the same as the hydrogen had been pumped out mechanically. The low vapor pressure of ice at the temperature of the liquid nitrogen refrigerant is not a significant factor in the vacuumchamber pressure. Even at temperatures as high as 200 K., the vapor pressure of ice is less than 0.01 mm. of mercury.

The operating conditions of. the above-described embodiment 13.1'6 believed to be within the range in which this invention would be found to be most useful, however, it is not intended that the aforesaid conditions include all limits of the operation and application of this invention. For example, if hydrogen gas is not admitted as a jet, the pressure recovery section is not required. Also, if the hydrogen gas is admitted cold then the chemical reaction can be induced by use of an external sou-Ice of heat, or by use of a catalyst such as platinum sponge.

A further embodiment of; the invention involves the reaction of gaseous material with one or more elements of a liquid or solid chemical compound in order to produce a third vaporous chemical compound which can thenbe frozen into a solid at much higher temperatures than the original gas. For example, gaseous hydrogen canbe combined with the oxygen in iron oxide to form water vapor. The water vapor is frozen by lowering its temperatureto such a degree that essentially all. of the water vapor condenses into-ice resulting in the production of} vacuumshaving: total pressures of less than millimeters ofjmercury,

Thisfuntherembodiment is best illustrated by referring to FIGURE 2 which depicts 'a system or vessel 60 to be evacuated. Evacuation, of the, vessel 601's accomplished by first evacuating the system with the aid of a small mechanical or diiiusion vacuum pump 62. During this initial evacuation period, a non-gaseous chemical 64, such as iron oxide, which has, been previously positioned Within a suitable container 66, is heated by means of a suitable electric heater 68. The initial heating is used in order to drive off any absorbed, adsorbed or occluded gases. The initial heating may or may not be required depending on the particular chemicals utilized to supply the oxygen. When the system is cleared of the casein tially no n-condensi-ble gases, valve 70 may be closed. However, under conditions where gases such as nitrogen, neon, krypton and xenon are involved, the valve 70 may be kept open and the pump 62 kept in operation. When there'are no other gases remaining in the system then hydrogen is introduced into the system from a suitable source 72, The source 72 may be an object in a test chamber such as arc-jet, or an externalsource such as a piping system. The small straight arrows, la eled H indicate the flow. of gas released from the source '72, The hydrogen reacts with the iron oxide, heated to red heat with the temperature thereof cont-rolling the rate of reaction, and combines with the oxygen in the iron oxide to form water vapor. The heat'exchanger 74, which is cooled by the flow of water, or other suitable refrigerant, through inlet 76 and outlet '78, is utilized only when hot gases are evolved from the source 72. This raids in reducing the load on the cold trap surface Strand the cold freezing surface 86. The surface St) and the surface 36 :are cooled to operating temperature i by means of a suitable refrigerant flowing through inlet and outlet means 82, 84 88 and 90 respectively.

During the operation of this system, the chemical 64 should be raised or lowered to operating temperature by the time the cold surface 80. and freezing surface 86 are cooled to a degree sufficient to freeze the resultant water vapor. The water vapor, as represented by the wavy arrows, attempts to flow in all directions; but quickly comes into contact with the surfaces and 86 thereby forming ice and concurrently reducing the pressure in the chemical reaction vessel 92. The ice forming reaction which takes place principally on freezing surface is very rapid and the water vapor turns into ice almost instantly. The result is an effective vacuum pumping action which is capable of quickly removing large volumes of gaseous material from a vessel or system with the concurrent production of extremely low pressures.

An examination of the teachings of invention clearly discloses a novel concept for removing large volumes of gaseous materials from containers or vessels. A further advantage of this invention resides in the fact that this system is capable of producing very low pressures in addition to an effective pumping action.

Although the invention has been described by reference to specific embodiments, it is not intended that it be limited to those elements specifically disclosed. For instance, oxygen gas could be pumped and removed by allowing it to-react with hydrogen or many other elements. The required freezing temperature, of course, would be determined by the final compound formed as a result of the chemical reaction as well as its vapor pressure at a practical low temperatur Some chemicals could be frozen at normal atmospheric temperatures, especially where extremely low final pressures are not required.

It can be seen, therefore, that this invention provides a system which is particularly suitable for removing and pumping extremely hot gases, such as those evolved from anarc-jet under test operating conditions. The elimination of large and expensive booster pump units for vacuum pumping, together with the obvious advantages achieved by using conventional, readily available and relatively low cost equipment, is obviously of great value during this age of high speed space technology.

It will be understood by those skilled in the art to which the present invention pertains, that while the methods disclosed herein illustrate preferred embodiments of the invention, modifications, and alterations can be made without departing from the spirit and scope thereof, [and that all such modifications as fall within the scope of the appended claims are intended to be included herein.

What I claim is:

l. A method for pumping a gaseous material comprising the steps of heating a first gaseous material consisting essentially of hydrogen, mixing said first gaseous material with an evacuated closed vessel with stcichiometric proportions of a second gaseous material consisting essentially of oxygen which has been derived by raising. the temperature of iron oxide to red heat, reacting the resultant gaseous mixture to form a v-aporous reaction product, solidifying said vaporous reaction product to its solid state thereby reducing the pressure in said closed vessel to produce a pumping action.

2 A method in accordance with claim 1 wherein said vaporous reaction product is water, the solidification of Which is achieved by freezing. 

1. A METHOD FOR PUMPING A GASEOUS MATERIAL COMPRISING THE STEPS OF HEATING A FIRST GASEOUS MATERIAL CONSISTING ESSENTIALLY OF HYDROGEN, MIXING SAID FIRST GASEOUS MATERIAL WITH AN EVACUATED CLOSED VESSEL WITH STOICHIOMETRIC PROPORTIONS OF A SECOND GASEOUS MATERIAL CONSISTING ESSENTICALLY OF OXYGEN WHICH HAS BEEN DERIVED BY RAISING 